1. Field
The present disclosure relates to zoom lens systems, interchangeable lens apparatuses, and camera systems.
2. Description of the Related Art
In recent years, interchangeable-lens type digital camera systems (also referred to simply as “camera systems”, hereinafter) have been spreading rapidly. Such interchangeable-lens type digital camera systems realize: taking of high-sensitive and high-quality images; high-speed focusing and high-speed image processing after image taking; and easy replacement of an interchangeable lens apparatus in accordance with a desired scene. Meanwhile, an interchangeable lens apparatus having a zoom lens system that forms an optical image with variable magnification is popular because it allows free change of focal length without the necessity of lens replacement.
Zoom lens systems having excellent optical performance from a wide-angle limit to a telephoto limit have been desired as zoom lens systems to be used in interchangeable lens apparatuses. Various kinds of zoom lens systems each having a negative lens unit located closest to an object side, and a multiple-unit construction have been proposed.
Japanese Laid-Open Patent Publication No. 2001-343584 discloses a zoom lens having a four-unit construction of negative, positive, negative, and positive, wherein the third lens unit moves in a direction along an optical axis to perform focusing from an infinity in-focus condition to a close-object in-focus condition.
Japanese Laid-Open Patent Publication No. 2008-191301 discloses an imaging optical system having a three-or-more unit construction of negative, positive, and negative, or negative, positive, and positive, wherein a lens unit having negative optical power is located on the object side relative to a diaphragm, and the lens unit having negative optical power has a cemented lens composed of a plurality of lenses.
Japanese Laid-Open Patent Publication No. 10-133106 discloses a zoom lens having a four-unit construction of negative, positive, negative, and positive, wherein a meniscus lens with the convex surface facing the object side is located on the most object side of the third lens unit, which has negative refractive power or weak positive refractive power, and the fourth lens unit has at least two positive lenses.